The present invention relates generally to integrated circuit die testing and more particularly to apparatus for performing static and dynamic tests on integrated circuit devices at various temperatures.
Completed integrated circuit devices on a semiconductor wafer are subjected to a variety of tests to determine which devices function properly so that inoperative devices can be removed from further processing. It is not unusual for the cost of assembling and packaging the die to greatly exceed the cost of the die itself, especially in the case of high reliability devices. Therefore, significant savings in assembly, packaging and final testing can be achieved by screening out unacceptable devices immediately after wafer fabrication is completed.
The testing of a die on a completed wafer, or multiprobe testing, is generally performed at about 25.degree. C. by coupling logic test signals to the inputs of the die and sensing the output signals to determine that the device switches properly. This is referred to as static or "DC" testing since low frequency logic input signals are used and the outputs are sensed after the device reaches a steady-state condition. While the static test is important in predicting whether a device will be operable following assembly and packaging, it does not insure that a completed device will pass a final test which simulates operation at normal operating frequencies and switching speeds. It is thus desirable to perform dynamic or "AC" tests to more accurately predict which die will pass a similar final test after completion. Dynamic testing includes the application of high speed logic signals to the die while sensing the outputs to measure operating parameters such as propagation delay times and swtiching speeds under predetermined load conditions.
The operability of a completed device at final test can be further insured by static and dynamic multiprobe testing of the die at elevated and lowered temperatures, for example, greater than about 70.degree. C. and less than about 0.degree. C. However, the accuracy and repeatability of high temperature tests are limited by the thermal effects on various components of the system. A typical probing system includes a plurality of extremely thin metallic probe mounted on a probe support such as a printed circuit board and arranged in a pattern identical to the contact areas on the die to be tested. The system further includes a semiconductor wafer chuck for positioning a wafer thereon to successively place each die into contact with the probes. A single probe is about 1 mil in diameter and must accurately contact an area on a die that is about 3 mils on the side. For most probes the angular positioning accuracy must be within about .+-.1/4.degree..
The thermal expansion and contraction of the probes and the probe support causes movement of the probe tip, which in turn can cause the probes to intermittently lose contact with the die under test, or to move outside of the acceptable test area on the die surface. This probe movement can cause operable devices to be improperly rejected.